Sometimes you need to get into a computer without knowing the password. Perhaps you've forgotten yours, or perhaps you're up to no good. Either way, it's actually pretty easy to do, provided your victim hasn't taken the necessary precautions. Click one of the links below to find out how to do it on either a Windows PCor a Mac, and how to prevent others from doing the same to you.

This classic post has been republished is part of our Evil Week series at Lifehacker, where we look at the dark side of getting things done. Knowing evil means knowing how to beat it, so you can use your sinister powers for good. Want more? Check out our evil week tag page.

Even if you aren't a sinister evildoer, there could be times when you need to get into a computer without the password. It's quite easy to do on a Mac, and learning how to do it can help you keep yourself better protected, too. Read more...